A conventional thermoplastic polyester elastomer (hereinafter, referred to as “TPEE”) has been used for electric, electrical, automobile, industrial and various precision parts and the like due to superior heat resistance, chemical resistance, dimensional stability and flexibility. In recent years, plasticizing is underway in the automobile field due to weight reduction and TPEE is employed in blow molded articles such as air ducts, constant velocity joint boots, rack & pinion boots and bellows.
TPEE is widely used in electric/electrical, automobile and industrial fields due to superior low-temperature impact properties and excellent oil resistance, chemical resistance and mechanical properties and is an elastomer used for engineering-based parts, together with a thermoplastic urethane elastomer and a thermoplastic polyamide elastomer. A representative example of the TPEE is a polyetherester-based block copolymer resin composition and TPEE is generally prepared by a melt polycondensation process.
In particular, parts such as automobile air ducts, constant velocity joint boots and various bellows should have optimum melt viscosity and melt tension in a melt state, since they are produced by blowing melt TPEE. In addition, the parts are generally known to be produced by reaction extrusion of a TPEE-based resin obtained by melt polymerization, since it should have a parison property in which a thickness distribution of a molded article is uniform during blowing.
Because general TPEE is inapplicable to blowing due to low melt viscosity and low melt tension in a melt state, there is a limitation in obtaining a polymer having a sufficiently high melt viscosity when produced by melt polycondensation. In addition, although a polymer is prepared by performing melt polycondensation for a predetermined time, in many cases, physical properties of the polymer are deteriorated. Accordingly, an attempt to improve melt viscosity of TPEE was actively made for a long time ago. Japanese Patent Publication Sho. 49-13297 discloses a solid-state polymerization method to increase a polymerization degree of TPEE obtained by melt polymerization. The obtained resin greatly depends on a retention time of melt viscosity and involves great variation in molding conditions upon re-molding after molding, thus disadvantageously requiring control.
In addition, an attempt to increase a melt viscosity to a level, enabling blow molding, by blending TPEE with a cross-linking agent or a chain extender was made. In a case in which an isocyanate-based compound is used as the chain extender agent, it is not easy to control reaction during reaction extrusion and to manage and store the reaction product in a liquid phase, reactivity is deteriorated due to reaction with moisture and it is not easy to control great difference in physical properties between lots during reaction extrusion reaction due to excessively high speed of isocyanate with moisture (Japanese Patent Publication Sho 52-121699, Japanese Patent Publication Sho 57-78413, Japanese Patent Publication No. 2005-325220, U.S. Pat. No. 5,733,986 and the like).
In addition, when a carbodiimide compound (referred to as polycarbodiimide compound having two or more N═C═N— units in a molecule) is used, a great amount of expensive polycarbodiimide compound should be used so as to obtain high melt viscosity and parison stability. In particular, an operation environment is not preferred because of unique odor derived from a high content of volatile organic compound during a molding operation upon chain extension by reaction extrusion between a polyester resin and an imide group (see Japanese Patent Publication No. 2011-94000).
In addition, when an epoxy resin is used, reactivity is greatly changed according to epoxy equivalents and the number of functional groups, and there are problems associated with reactivity and handling such as dispersion of an epoxy resin in a resin and effects of moisture during storage (see Japanese Patent Publication No. 11-323110, Japanese Patent Publication No. 2000-239354, Japanese Patent Publication No. 2000-355650 and Japanese Patent Publication No. 2001-247752).
Furthermore, when an oxazoline compound is used, an effect on improvement in molecular weight may be deteriorated due to low reactivity as compared to an isocyanate compound, an epoxy resin and a carbodiimide compound.